Adjustable iris

ABSTRACT

A variable aperture iris located at a waveguide T-junction. Two sliding gates and their related positioning members are of a suitable configuration to form a smooth continuous surface along the waveguide for all sizes of aperture opening.

nited States Patent Inventor Leslie Gaza Varhelyi Ottawa, Ontario,Canada Appl. No. 841,693 Filed July 14, 1969 Patented May 4, 1971Assignee Northern Electric Company Limited Montreal, Quebec, CanadaADJUSTABLE IRIS 5 Claims, 4 Drawing Figs.

US. Cl 333/98, 333/73, 74/1 10,251/212 1nt.Cl H01pl/00, HOlp 5/04, F16k3/03 Field of Search 333/98, 985, 83, 73 (W), 73, 3,000; 251/205, 212,326; 74/ 1 10 Primary Examinerl-lerman Karl Saalbach AssistantExaminer-Wm. H. Punter Att0rneyWeir, Marshall, MacRae & Lamb ABSTRACT: Avariable aperture iris located at a waveguide T-junction. Two slidinggates and their related positioning members are of a suitableconfiguration to form a smooth continuous surface along the waveguidefor all sizes of aperture opening.

PATENTEU MAY 4197:

SHEET 1 [IF 2 PATENT AGENT vmmenm 4m: 3.577.106

SHEET 2 UF 2 PATENT AGENT ADJUSTABLE [ms BACKGROUND OF THE INVENTIONThis invention relates to a variable aperture iris providing couplingbetween two waveguides. .It is known that the susceptance of a waveguidecan be varied by inserting conductive diaphragms or irises in thewaveguide. The added susceptance is inductive or capacitive depending onwhether the added material is parallel or orthogonal to the electricfield vector. The magnitude of the added susceptance depends on thedimensions of the added material, i.e., the size of the aperture definedby the iris.

One type of waveguide filter uses several cavities connected in shuntwith the main waveguide, the coupling between the main waveguide andeach cavity being controlled by an positioned at the junction. Insetting up such filters, and in particular in performing susceptancemeasurements, difficulties arise due to the large number of readingsrequired at differing sizes of iris aperture. Such measurements havegenerally been performed by disassembling the filter structure to insertfixed irises of different sizes.

SUMMARY OF THE INVENTION Briefly, the structure of the variable iris ofthe present invention consists of two slidable gates each having asmooth wall forming a portion of the sidewall of the main waveguide. Apositioning member of wedge-shaped configuration is provided for eachgate. Each positioning member has a smooth surface and a notchedsurface. The notched surface engages with a corresponding notchedportion in the respective gate to effect movement thereof while thesmooth surface abuts on the smooth surface of the gate forming a furtherportion of the waveguide wall.

Such structure is particularly useful in setting up microwave filters ofthe type described in the preceding section in that there is norequirement 'to disassemble the filter in order to change the aperturesize of the iris. Calibration markings may be provided on thepositioning members which indicate accurately the corresponding apertureopening.

BRIEF DESCRIPTION OF THE DRAWINGS DESCRIPTION OF THE PREFERREDEMBODIMENT A particular embodiment of the invention used in conjunctionwith a waveguide T-junction will be described in conjunction with FIGS.1 through 4. With particular reference to FIGS. 1 and 2, a T-junction isformed between a main waveguide and a secondary waveguide 11. Secondarywaveguide 11 is intended for use as a resonant cavity and a conventionaltuning plunger 19 is provided.

The coupling between main waveguide 10 and secondary waveguide 11 isadjustable by means of a variable iris structure positioned at theentrance 12 of the secondary waveguide. To provide this variable irisstructure, a section of the sidewall of the main waveguide is recessedbetween surfaces 31 to form a support surface 32. Supporting members I5and I6, which are extensions of the sidewalls of the secondary waveguideII, extend beyond support surface 32 toward the plane of the sidewall ofthe main waveguide. Slidable gates 13 and 14 provide the variableaperture in the iris structure. Gate 13 has a smooth wall portionbridging parallel legs 26 and 27. These legs are substantially square incross section and are slightly displaced from the plane of smooth wall20 to form therewith a pair of shallow grooves 33 and 34. In theassembled condition gate 13 is positioned for slidable movement abuttingon support surface 32 with legs 26 and 27 engaged on either side ofsupporting members 15 and 16. In this position,

wall surface 20 lies in the plane of the sidewall of the main waveguide,that is, it is coplanar with surfaces 31.

Gate 14 has a smooth wall surface 21 coplanar with legs 22 and 23. Gate14 is positioned for slidable movement abutting on gate 13 with legs 22and 23 engaged in shallow grooves 33 and 34, respectively. When sopositioned, wall surface 21 also forms a portion of the sidewall of themain waveguide being coplanar with fixed wall surfaces 31 and wallsurface 20 of gate 13.

Thus, it will be seen that in the structure so far described, gates I3and 14 are movable to form the variable i'ris which controls the degreeof coupling between the main waveguide 10 and the secondary waveguide11. When the iris aperture is partially open, as in normal operation,portions of grooves 33 and 34, designated 37 in FIGS. 2 and 3, formhollow spaces in the assembled structure. It will be noted, however,that spaces 37 are outside waveguides 10 and 11 and do not provide anydiscontinuity to affect wave propagation.

The movement of gates 13 and 14 is controlled by positioning members 17and 18, shown in greater detail in FIGS. 3 and 4. Each positioningmember is of a tapered or wedge-shaped configuration and has a smoothsurface 35 and an opposed notched surface 36. Corresponding notchedportions 24' and 25 are provided at the end of gates 13 and 14respectively. In the assembled position of the variable iris, eachpositioning member is located with the notched surface 36 engaging withone gate notched portion and the smooth surface positioned in the planeof the sidewall of the main waveguide. Movement of the positioningmembers in the plane of the sidewall of the waveguide producescorresponding movement of the gates and hence variation in aperturesize.

It will be noted that the sidewall of the main waveguide is completelyfree from discontinuities and obstructions. That is, in the region ofthe variable iris, the wall is formed by surfaces 31, smooth surfaces 35of the positioning members, and surfaces 20 and 21 of the movable gates.Similarly, the. walls of the secondary waveguide 11 are unobstructed,being defined in the region of the variable iris by supporting members15 and I6 and legs 26 and 27 of gate 13.

Positioning members 17 and 18 are connected for simultaneous movement bya crossbar 28 which is, in turn, attached to an apertured plate 40.Plate 40 engageswith flanges 44 on an internally threaded hand wheel 42mounted for movement along a lead screw 41. Lead screw 41 is supportedby base 43 on the upper surface of the waveguide assembly. Furtherguiding members 45, which may be generally similar to I7 and 18, areprovided at the other side of the main waveguide from positioningmembers 17 and I8 in order to eliminate twisting and side pressure. Inone form of the present invention a pair of resonant cavities areprovided on either side of the main waveguide. For this situationguiding members 45 become the positioning members of a further variableiris located (with reference to FIG. 2) in the left-hand sidewall ofwaveguide 10.

It will be realized that the extent of the aperture opening in the iriscannot be observed when the apparatus is in its assembled condition. Theopening is, however, directly related to the vertical displacement ofthe positioning members and suitable visible calibration indicia may beplaced on them and on flange 44 of handwheel 42, as shown in FIGS. 2 and4.

I claim:

1. A variable iris positioned in a wall of a main waveguide comprising:

a support surface spaced from the plane of said waveguide wall defininga fixed aperture.

supporting members extending from said support surface toward the planeof said waveguide wall,

a first gate having a projecting smooth wall at one side thereof andspaced guiding members positioned abutting on said support surface forslidable movement with the guiding members engaging the supportingmembers and said smooth wall forming a portion of the waveguide wallpartially covering said fixed aperture,

'a pair of positioning members, one for each gate section,

each having opposed smoothand notched surfaces positioned with saidnotched surfaces engaging with notched I portions on said gates and thesmooth surfaces forming further portions of said waveguide wall, wherebymovement of said positioning members moves said gates to alter theopening of the variable iris,

the smooth walls of said gates and the smooth surfaces of saidpositioning members forming a substantially unbroken coplanar surface 2.A variable iris as defined in claim I wherein said support surfacedefinesa further waveguide forming a tee junction with the mainwaveguide and the variable iris alters the coupling between said mainwaveguide and said further waveguide.

3. A variable iris as defined in claim 2 wherein said supporting membersare extensions of the sidewalls of the further waveguide and the guidingmembers of said first gate consist of a pair of spaced apart parallellegs.

4. A variable iris as defined in claim 3 wherein the guiding members ofsaid second gate are a pair of spaced apart parallel legs received inchannels in said first gate.

5. A variable iris as defined in claim 1 wherein said positioningmembers are of tapered configuration.

1. A variable iris positioned in a wall of a main waveguide comprising:a support surface spaced from the plane of said waveguide wall defininga fixed aperture. supporting members extending from said support surfacetoward the plane of said waveguide wall, a first gate having aprojecting smooth wall at one side thereof and spaced guiding memberspositioned abutting on said support surface for slidable movement withthe guiding members engaging the supporting members and said smooth wallforming a portion of the waveguide wall partially covering said fixedaperture, a second gate having a smooth wall at one side thereof andspaced guiding members positioned abutting on and engaged with saidfirst gate section for slidable movement, the smooth wall of said secondgate forming a further portion of the waveguide wall partially coveringsaid fixed aperture, a pair of positioning members, one for each gatesection, each having opposed smooth and notched surfaces positioned withsaid notched surfaces engaging with notched portions on said gates andthe smooth surfaces forming further portions of said waveguide wall,whereby movement of said positioning members moves said gates to alterthe opening of the variable iris, the smooth walls of said gates and thesmooth surfaces of said positioning members forming a substantiallyunbroken coplanar surface.
 2. A variable iris as defined in claim 1wherein said support surface defines a further waveguide forming a teejunction with the main waveguide and the variable iris alters thecoupling between said main waveguide and said further waveguide.
 3. Avariable iris as defined in claim 2 wherein said supporting members areextensions of the sidewalls of the further waveguide and the guidingmembers of said first gate consist of a pair of spaced apart parallellegs.
 4. A variable iris as defined in claim 3 wherein the guidingmembers of said second gate are a pair of spaced apart parallel legsreceived in channels in said first gate.
 5. A variable iris as definedin claim 1 wherein said positioning members are of taperedconfiguration.